1. Field of the Invention
This invention relates to a heat-resistant plastic container which can undergo retort treatment and has a high gas barrier property, thereby protecting food contained therein from putrefaction or oxidation even during storage at a room temperature and being excellent in capability for a long-term storage, and which at the same time can undergo heating in a microwave or in an electric cooking oven while containing food without transferring the content into a different container.
2. Background of the Invention
Recently, as the home use of electric cooking ovens as well as microwaves are being wide-spread, requirements for plastic containers to be usable in the both ovens ("dual-ovenable") have been enhanced. As resins usable in electric cooking oven (220.degree. C.), crystalline polyester (hereinafter referred to as PET), polyetherimide, and the like are known; and in particular, containers utilizing crystalline PET have been put to practical use. However, conventional PET containers cannot, since they are lacking both in retortability (capability for retort treatment) and in gas barrier property, be used for containers for transporting and storing foods at a room temperature, and their uses therefore have been limited.
Multi-layer containers made of polypropylene and a gas-barrier resin have been used for containers being capable of retort treatment and having gas barrier properties. As such gas-barrier resins, ethylene-vinyl alcohol copolymer (hereinafter referred to as EVOH) or polyvinylidene chloride resins have been used. However, multi-layer containers utilizing polypropylene have, though usable in microwaves, no heat resistance against electric cooking ovens.
U.S. Pat. No. 4,425,410 discloses a retortable multi-layer structure comprising an EVOH layer containing a drying agent and a polyolefin layer provided thereon, but does not state about providing a crystalline PET layer on an EVOH layer containing a drying agent.
Unexamined Japanese Patent Laid-Open No. 62660/1984 discloses an ovenable container comprising a crystalline PET, but does not state about a container comprising a crystalline PET layer and an EVOH layer or an EVOH layer containing a drying agent provided thereon.